The basic message during the Web video giant’s presentation—which doubled as a 10th birthday party for the service—was, essentially: our stars are influential, our viewers are young, they favor consuming media on mobile devices, and they are never going to watch TV the way that previous generations did.

YouTube’s head of content and business operations, Robert Kyncl, noted the recent surge in cable TV cord-cutting options by evoking Ernest Hemingway’s famous line from "The Sun Also Rises" about going bankrupt gradually, then suddenly.

“For 60 years, Hollywood has owned the living room,” he said. But in five years, Mr. Kyncl predicted, the majority of ad-supported video viewing will occur on mobile devices. “That shift requires partnering with a new set of players.”

Naturally, that would include YouTube. Already, the company’s mobile audience for adults between 18 and 49—the ad community’s sweet spot--is larger than any cable network's, executives said, citing a Google commissioned Nielsen study covering the period of December of 2013 to February 2015.

That sort of talk was a far cry from several years ago, when YouTube used its NewFront event to trumpet its growing relationship with a slew of Hollywood stars. But over the past few years, YouTube has embraced the idea that it has birthed a new generation of talent and content types—and advertisers need to get on board.

For much of the night, YouTube walked the advertisers and agency executives through different content genres, from comedy to cookin, that fall into the premium “Google Preferred” sales bucket, which is aimed at setting aside the most desired YouTube content for brands. Presenters included BuzzFeed’s president of motion pictures, Ze Frank, YouTube comic Grace Helbig and gaming enthusiast Justine Ezarik.

Ms. Helbig was one of several speakers who took subtle shots at Facebook’s video explosion, which has been driven in large part by the fact that videos on Facebook play automatically in people’s news feeds—often on mobile devices. When people see an ad on YouTube, Ms. Helbig said, they are “not just passively seeing it as they scroll by.”

But perhaps the most memorable moment of the night was an appearance by Mr. Green, whose novel “The Fault in Our Stars” was inspired by a teen cancer victim he met via YouTube, who practically scolded advertisers into buying more ads on YouTub, less they miss out on an entire generation.

“Lots of online video is well-supported by advertising.. but most [content] is dramatically underfunded,” he said. That’s led many creators toward “building a world where they don’t have to depend on advertising and they are thriving.”

Mr. Green argued that while TV shows like "CSI Miami" are great “distraction” for many Americans, YouTube viewers exhibit a different level of engagement and passion. “We are not in the distraction business,” he said. “We are in the community business.” And brands that don’t realize that soon will be left behind.

But for the most part, the night was upbeat, particularly the closing musical performance by Bruno Mars, who performed the single "Uptown Funk," which appropriately features the line "don't believe me just watch."